Ultraviolet materials are well-suited for use as inks and resins for printing optically readable codes, such as optical character recognition, bar codes, matrix codes and other one-dimensional and multidimensional symbologies, because an ultraviolet material is excited and fluoresces when ultraviolet light strikes it. The fluorescent light emitted by the ultraviolet material may then be detected, that is photographed or imaged with a camera or CCD device, and the captured information decoded and processed.
Ultraviolet printing materials provide a further benefit that, compared to nonultraviolet printing inks or fluorescent materials, they can be more readily applied directly on a greater variety of substrates, such as glass as in the case of glass vials or test tubes. More particularly, printing ultraviolet optically readable codes directly on a surface eliminates the need to print an optically readable code on a paper label which must then be applied to the substrate.
An especially useful type of binary code is a matrix code as described in detail in U.S. Pat. No. 5,324,923, which is incorporated by reference herein. Matrix codes are more compact and can contain more information than other binary codes (making them especially suitable as identifiers on small test tubes). Matrix codes can also be made very reliable.
To cause the ultraviolet material to fluoresce sufficiently to be read by a nearby camera requires light intense enough to illuminate and facilitate the capture of all of the coded information. Unlike ordinary incandescent lamps, a strobe lamp is known to provide a high intensity flash with a sufficient quantity of ultraviolet light to cause the requisite fluorescence. The fluorescent light emitted by the ultraviolet material may be the same color as the ink in a nonfluorescent state.
A conventional strobe lamp, however, emits an undesirable amount of nonultraviolet light which interferes with the fluorescence of the ultraviolet material. Moreover, the ultraviolet light may also cause other fluorescent materials, which do not contain coded information and which are not the intended target for the fluorescence, to fluoresce and thereby generate additional fluorescent light which interferes with the reading of the optically readable code.